Feed control for mills



Feb. l1, y1936. R. M. HARDGROVE FEED CONTROL'FOR MILLS Original FiledMay 29, 1928 5 Sheets-Sheet 1 ,/HINVENTOR ATTOR NEYJ Feb. 1l, 1936. R.M. HARDGRovE 2,030,448 l yFEED' CONTROL EoR'MILLs original Filed My 29,192e s sheets-sheet 2 2 Mm. speso y FIGS FEEDER SPEED ATTORNEY:

Feb. 11,1936. I RIM. HARDGROVE l 2,030,448

FEED CONTROL FOR MILLS Original Filed May 29, 1928 3 Sheets-Sheet 3)2J/wo aWBY funk @W am mental Fel.. 11, 193e UNITED STATES FEED CONTROLFOR MILLS Ralph M. Har'dgrove, Bethlehem, Pa., assignor to Fuller LehighCompany, Fullerton, Pa., a corporation of Delaware Application May 29,192s, serial No. 281,565

Renewed July 30, 1932 8 Claims.

This invention relates to a device by means of which the feed ofmaterial to a grinding mill is automatically controlled by the amount ofmaterial in the mill that is being ground. 'I'he 5 invention isespecially applicable to grinding mills for pulverizing coal but is notrestricted to this particular use.

'Ihe invention .will be understood from the description in connectionwith the accompanying drawings in which Fig. 1 is a vertical sectionthrough an illustrative embodiment of theinvention; Fig. 2 is a sectionpartly brokenl away at right angles to Fig. l; Fig. 3 is a verticalsection similar to Fig. 1 showing a modification;

5 Fig. 4 is a section similar to Fig. 2 `showing a modification of someof the details; Fig. 5is a diagrammatic view showing relations betweenthe speed of the mill and the speed of the feeder; Fig. 6 is a verticalsection similar to Fig. 1 shown ing another modification; Fig. 7 is asection at right angles to Fig. 6 showing some of the details on anenlarged scale; and Fig. 8 is a plan view on an enlarged scale showingsome of the details.

5 In the drawings reference character I indicates a grinding mill forcoal or the like that is provided with grinding balls 2 that rest upon`and are driven by a disc 3 that is in turn driven by gear mechanism 4by means of the motor 5. 0 A shaft 6 is journaled in bearings in theside wall of the mill I and is provided with a depending arm 1 at theinner end thereof. The lower end of the arm I extends into proximitywith the upper surfaces of the grinding balls 2 5 and is apt to bestruck by the material that is being ground and pushed to the side toturn the shaft 8 when the material reach a certain depth or accumulatesto a certain extent while being ground. A switch 8 is connected to the 0shaft I to make and break contact in an electrical circuit in accordancewith the position of the arm 1. The switch 8 is shown as a mercoidswitch in which the make and break is made by tilting the switch backand forth. Il A coal feeder IIl is somewhat diagrammatically shown andfeeds coal through the inlet II at the upper portion of the mill I.'I'he coal feeder I l is driven by a shunt motor I2 and the rate of feedis governed by the speed of the' motor. 0 The electric mains areindicated at I3 and a Aresistance Il is connected in series with theshunt field I5 of the motor. A short circuit Il is provided around theresistance `Il and is open and closed by means of the switch Il. t Theoperation is as follows: 'I'he resistance I4 is adjusted so that thespeed of the motor AI2 will be slightly greater than is necessary tofeed the coal at the proper rate to the grinding mill.. When the coalthat is being ground accumulates a suicient amount tof strike the arm'I, the 5 switch B is closed, thereby short circuiting the resistance I4inseries with the shunt field I5 .of the motor I2 and causing the motorto slow down. When the level of the coal that is being ground descends,the arm I turns back by grav- 10 ity and opens the switch B therebySpeeding up the motor I2.

In the modification shown in Fig. 3 another resistance I8 is connectedin series with the resistance Il and shunt'leld I5 of the feeder motorI2. 15 The effective portion of the resistance I8 can be varied by amovable arm I9, the position of which is changed in accordance withchanges in the amount of fuel required in the associated furnace. T 'hechanges in position of the arm I9 are auto- 20 matically controlled inthe modification shown in Fig. 3 by meansfof a suitable combustioncontrol device, diagrammatically'illustrated at 20, fresponsive to acondition or quantity, such as boiler steam pressure, varying with theamount of fuel supplied to the furnace. The arm I9 is controlled v bythe combustion control device 20* through a chain and sprocket drivelconnection 2Il'so that any adjustment of the control device 20* willautomatically adjust the resistance I8, and thereby vary the speed ofthe motor I2 and the rate at which the coal is fed to the mill. Thecontrol device 20 is also used to simultaneously control the speed ofthe mill motor 5 through a chain andy sprocket connection 20 to a drumcontroller 2l and 36 electrical connections 22, as diagrammaticallyillustrated in Fig. 3. 'I'he drum controller 2| may. be of any wellknown type capable of variably controlling the speed of rthe motor 5. Inthis way an adjustment of the combustion control device 40 l0l not onlyregulates the speed of the motor E driving the mill I but also regulatesthe speed of the motor I2 driving the feeder III. Besides. when theswitch B is closed by an accumulation of material in the mill I, asdescribed in connection with 1, to short circuit the switch Il, andthereby slow down the feed motor I2, the

vspeed of the feeder III will be reduced but not entirely to the minimumspeed so that there is less shock on the feeder motor I2 as it isreduced 60 only enough to obtain the desiredamount of control. The upperline in Fig. 5 shows the relation between the speed of the feeder andthe speed of the'mill when the feeder is feeding more rapidly than themill is grinding. The middle line repre- 55 sents the relation when thetwo speeds have been adjusted so that the grinding is at the same rateas the feed and the lowest line represents the relative speeds of thefeeder and mill when the switch 3 has been closed to slow down thefeeder motor I2.

Instead of mounting the mercoid switch 3 directly upon the shaft 6, thisswitch may be pivoted independently and connected by means ofthespring23toanarm2l ontheshafti asshown in Fig. 4, and a dash pot 25may be connected to the arm 26 to make the operation more smooth. In themodification shown in Figs. 6, l and 8 the vfeeder control is entirelymechanical. In this modlcation a worm 23 is provided on the shaft of thedriving motor and drives a shaft 23 that is provided with a crank pin 30to which a rod 3| is connected. The other end of the rod 3l is connectedto one end of a pivoted lever 32, the other end of which carries thepawl 33, which upon being oscillated drives the gear 3| by Imeans ofwhich the roller 35 of the feed mechanism 36 is driven. The feedmechanism consists of a belt passing over rollers by means of which thecoal .is fed to the mill I. The outer end of the shaft 6 to which thearm 1 is attached carries an arm 31 to the outer endof which one end ofa .rod 38 is connected, the other end of this rod 33 being connected toa cam 33 that is pivoted on the same pivot as the lever 32. The camsurface III moves under the pawl 33 and lifts the same so that it willnot contact with the teeth 34 when the level of the coal in the mill Irises suflciently high to strike the arm 1, thus stopping the feed ofthe coal until the arm 1 descends and turns the shaft 8 suf-` ciently topermit the pawl 33 to contact again with the teeth 3l.

The embodiment of the invention illustrated in Figs. l and 2 isespecially suitable for storage system preparation plants where thegrinding mills are operated at their maximum capacities all of the time,and coal level control is required only to insure that the mills arebeing supplied with coal' at the maximum rates at all times, thus noteither choking or suffering a loss in capacity. The embodimentillustrated in Figs. 3 to 5 is especially useful in a unit fired millwhere the mill speed is to be varied forydifferent capacities,` and thefeeder speed would also have to vary over a much wider range than wouldbe necessary for storage system plants. 'I'he embodiment shown in Figs.6 to 8 is well adapted either to storage or vunit red operation.

I claim: p

1. In a device for controlling the rate of feed to a ball mill having aseries of horizontally rotating grinding balls. and drive meanstherefor, a feed mechanism, and means independent of said drive meansand operated by the depth of material in the mill to control the feed`mechanism.

2. In a device for controlling the rate of feed to a ball mill, a feedmechanism, a series of horizontaliy rotating grinding balls, and meanscomprlsing a pivoted arm operated by the depth of material in the millto control the speed of the feed mechanism. 5 3. In a ball mill forgrinding coal, a coal feeder, a series of horizontally rotating grindingelements and means comprising a pivoted arm and an electrical make andbreak switch operated by the level of coal on said elements to controlthe speed of the feed mechanism.

4. In a grinding mill, a grinding ring, a row of grinding elements, anarm pivoted above the upper surface of said elements as they operate,and means connected to said arm for controlling the operation of saidmill.

5. In a mill for grinding coal, a coal feeder, a series of horizontallyrotating grinding elements, means for rotating said elements, means fordriving said coal feeder comprising a pawl, in driving relation to saidcoal feeder and in driven relation .to said element rotating means, aratchet operated by said pawl, and a pivoted lever connected to saidpawl and operated by the level of the coal on said elements to controlthe engagement of said pawl and ratchet.

6. In a device for controlling the rate of feed of material to a millhaving a series of horizontally rotating grinding balls, a feedmechanism, and means comprising a pivoted arm responsive to the depth ofmaterial being ground in said mill for controlling said feed mechanism.

'7. In a grinding mill having a stationary mill casing, a grindingsurface within said casing, a series of rolling grinding elementscontacting 35 with said surface. means forming'a space in said mill forthe accumulation of material in the course of grinding, drive means foreffecting a relative movement between said grinding elements and saidsurface. a feed mechanism, sepau rate drive means for said feedmechanism. means responsive to changes in a variable quantity aifectedby the operation of said mill for simultaneously controlling theoperation of both of said drive means, and means responsive tothe amount4'5' of material in said space for independently controlling theoperation of said feed mechanism drive means.

8. In combination, a mill for puiverizing solid fuel, means for drivingsaid mill, a feeder for 5o delivering fuel to be pulverized to saidmill,l means independent of said mill driving means for driving saidfeeder, automatic control means responsive to changes in a variablequantity affected by changes in the amount of pulverized fuel dischargedby said mill arrangedto control the operation of said mill and feederdriving Y. means, and automatic control means operable independently ofsaid first mentioned control means to control the operation of saidfeeder in RALPH M. HARDGROVE.

